1. Field of the Invention
The present invention relates to a timepiece dial plate and, more particularly, to a timepiece dial plate provided on its face with relief indices resembling characters and such.
2. Description of the Related Art
Referring to FIG. 10, a timepiece dial plate 100 is provided on its face with indices including hour markers 102 and a name marker 103. The time piece dial plate 100 is fixedly provided with two positioning legs 101 so as to project from the back surface of the timepiece dial plate 100. The two positioning legs 101 position and fix in place the timepiece dial plate 100 relative to a movement. Various finishing methods are applied to the manufacture of luxury timepieces to finish their indices including hour markers beautifully. For example, a timepiece dial plate 100 as shown in FIG. 11 is provided with indices including hour markers 102 set on the face thereof by a setting method. The setting method forms hour markers 102 having various facets individually, and sets each of the hour markers 102 on a timepiece dial body by fitting legs 102a formed on the hour marker 102 in holes formed in the timepiece dial body of the timepiece dial plate 100. The indices thus attached to the timepiece dial plate 100 assume a fully solid appearance.
Those indices, however, need high manufacturing costs because the indices must individually be subjected to many processes to form the facets. Since the facets are limited to flat surfaces, the indices are unable to assume a solid appearance having optional curved surfaces.
An electroforming method is another method of manufacturing a timepiece dial plate provided with fully solid indices. An electroforming method deposits a metal on a pattern by electrodeposition and separates a metal coating formed over the pattern from the pattern to obtain an electroformed article having a shape exactly resembling that of the surface of the pattern. Electroforming is capable of forming facets of indices, such as hour markers, not only in flat surfaces but also in optional curved surfaces.
An electroforming process for forming a timepiece dial plate will be described with reference to FIG. 12 by way of example.
A model 110 (male pattern) as shown in FIG. 12(a) exactly resembling a timepiece dial plate to be manufactured is formed. In FIG. 12(a), indices including hour markers are represented typically by a protrusion 105. As shown in FIG. 12(b), a plastic mother 111 (female pattern) of a plastic material is formed by using the model 110. The plastic mother 111 is separated from the model 110 as shown in FIG. 12(c), and a plurality of stampers 112 (male patterns) are formed by depositing an alloy of Cu and Ni or the like on the plastic mother 111 by electroforming. Then, as shown in FIG. 12(d), a number of plastic patterns 113 (female patterns) equal to the number of timepiece dial plates to be produced are formed by using the stampers 112 (male patterns). A timepiece dial body 115 for a timepiece dial plate 116 as shown in FIG. 12(f) is formed by electroforming using the plastic pattern 113. An electroformed member 114 is formed by using the plastic pattern 113 as shown in FIG. 12(e). The electroformed molding is separated from the plastic pattern 113, and the electroformed member 114 is cut along a cutting plane 114a to obtain the timepiece dial body 115.
Legs 117 for fixedly positioning the timepiece dial plate 116 relative to a movement must be welded or brazed to the timepiece dial body 115. The electroformed member 114 must be cut along the cutting plane 114a to form the timepiece dial body 115 having a flat back surface and a thickness t. Then, the legs 117 are welded or brazed to the flat back surface of the timepiece dial body 115 to complete the timepiece dial plate 116.
When manufacturing the timepiece dial plate 116 by the conventional electroforming method, the timepiece dial body 115 formed by an electroforming process secures rigidity and strength for the timepiece dial plate 116, and the legs 117 are welded or brazed to the timepiece dial body 115. Therefore, the back surface of the timepiece dial body 115 must be flat to facilitate welding or brazing the legs 117 thereto, and the timepiece dial body 115 must be relatively thick. However, the electroforming process needs several days to form a layer of several tens micrometers in thickness. Therefore, the electroforming process must be continued for several days, which increases the manufacturing costs of the timepiece dial plate greatly.